E

Feasibility of Decontaminating DredgedMaterial

C A FletcherT N Burt

Report SR 464March 1996

E"R wattingford

Address and Registered Office: HR Wallingford Ltd. Howbery Paft, Wallingford, Oxon OX10 8BATel: + 44 (0)1491 835381 Far + 44 (0)1491 832233

R€glrtd€d h Engbrd l.lo. 2562099. HR WaIirg'od i6 e wlE{y drEd sub6ilhry ol HR Wdfingtod Gd.p Ltd.

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trContract

This report describes work part-funded by the Department of the Environmentunder Research Contract Cl3915/94 for which the DoE nominated officer wasMr P B Woodhead and the HR nominated officer was Dr W R White. Thereport is published on behalf of the department of the Environment, but anyopinions expressed in this report are not necessarily those of the fundingDepartment. The HR job number was DBS 56. The work was carried out in thePorts and Estuaries Group at HR Wallingford under the management ofDr J V Smallman.

Prepared by S^u*'Sb(Job title)

Approved by T [I,..frry,r-

Date ..t.r../...2 rkc...

@ HR Wallingford Limited 1996

Cr^fi#*r(name)

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trSummary

Feasibility of Decontaminating Dredged Material

C A FletcherT N Burt

Report SR 46ztMarch 1996

Disposal options for contaminated dredged rnaterial are becoming morerestricted as pressure for decreasing inputs of contaminants to sea increases,and as landfill space reduces. Decontamination technologies whihc altercontaminated dredged material properties, such that they are suitable forbeneficial uses or sea disposal, are desirable. In this report the scale of thesituation is described through examples of contaminated dredged material inthe UK. A brief description of the international erperience of decontaminationtechnologies is given. The criteria which any prospective technology mustsatisfy in terms of practicality, effectiveness, economics and environmentalacceptability, as well as meeting legislative requirements, are outlined. Areview of the reported technologies for dredged matedal decontaminated isreported. This includes experience from a workshop titled "Decontaminationof Dredged Material" which was held at HR Wallingford.

Decontamination technologies are likely to need to handle large volumes ofmaterial with high water content and often mixtures of contaminants. Thesuitability of each technology will be site specific. There are many potentialtreatment technologies which are broadly categorised as mechanical, physico-chemical, biological and thermal treatments. Decontamination technologieshave the potential to become an integral part of the dredging and disposaloperation. However, only some of these technologies are proven at fullscale.Many which show potential are currrently underdeveloped and costly comparedto altemative methods such as containment. There is no 'cure-all' methodand the end solution is likely to involve a combination of treatmenttechnologies (treatment trains) and disposal options. Further research anddevelopment is required as decontamination technologies will be needed in thefuture in many countries. The export potential for developed technologies ishigh.

SR /164 1e/07rl6

trContents

Title pageContractSummaryContents

Page

33555666

l n t roduc t i on . . . .1.1 Background1.2 Objectives1.3 Report structure

The scale of the problem-quantitative and geographical . . .2.1 Dredged materialcontamination in the UK . . .2.2 Disposal options and constraints

2.2.1 Disposalto sea2.2.2 Disposalto land

2.3 Estuarine and coastal areas in the UK2.3.1 Devonport2.3.2 Blyth .2.3.3 Falmouth2.3.4 Portsmouth2.3.5 East Anglian Marina2.3.6 Newpaft2.3.7 Swansea2.3.8 Maryport2.3.9 Whitehaven2.3.10 The Tees Estuary2.3.11 The Tyne Estuary

2.4 lnland Waters in the UK2.4.1 North West Canal System2.4.2 Birmingham Canals2.4.3 Nortolk Broads2.4.4 Weaver Canal

2.5 Summary of UK Contamination

11't

2

223

666777777I8B

Criteria for a successful decontamination technology I3.1 Appropriate technology 93.2 Status and efficiency of technology . . 9

3.2.1 Development/ Availability 93.2.2 Sui tab i l i ty . . . . . . I3.2.3 Practicality (eg process capacity and

contact time) .3.2.4 Effectiveness

3.3 Costs and benefits3.3.1 Comparing clean-up costs with alternative

disposaloptions3.3.2 Environmental costs/ benefits .3.3.3 Changing legislation and emerging

regu la to r ysys tem . . . . . 113.3.4 Acceptability and public perception 11

I9

1 0

1010

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4.3

Review of technologies . '11

4.1 Definition of treatment for this study . 114.2 lnternational situation on decontamination

techno log ies . . . 12Reviewofdecontaminat iontechnologies . . . . 124.3.1 Background 124.3.2 Mechanical separation 134.3.3 Physico-chemical . 154 .3 .4 B io l og i ca l . . . . . . 184 .3 .5 Therma l . . 184.3.6 Costs of sediment decontamination

techno log ies . . . . . . . . . 20

D iscuss ionandConc lus i ons . . . . 21

Suggestions for further study

Acknowledgements

References

23

24

25

FiguresFigure 1Figure 2

PlatesPlate 1Plate 2

AppendicesAppendix 1Appendix 2Appendix 3

Decontamination TechnologiesSuitability of technologies with respect to maincontaminant chemical groups

The Slufter and "Parrots Beak", Rotterdam HarbourAmsterdam Canal clean-up using Hydrocyclone

Report on the Work ShopList of participantsCATS lll paper

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tr1 lntroduction

1.1 BackgroundThe dredging of navigational channels and waterways in the UK is aneconomically essential activity. The majority of material generated in the UKthrough essential dredging operations is inert in nature. However, thecontamination of sediments in some of our rivers, estuaries, ports andharbours, canals and marinas mean that the material dredged may haverestricted disposal options under UK legislation and licensing systems. Inaddition, the likely increase in legislative pressure preventing the disposal ofcontaminated sediments to sea may have serious implications for currentdisposal practices forsome dredged material. Alternative disposaloptions andbeneficial uses will be increasingly sought for contaminated dredged material.

The majority of materialfrom maintenance dredging is fine grained sediments(<63pm) which are cohesive in nature and thus, generally less appropriate forbeneficialuse projects. In addition, contaminants are often associated with thefine grained sediments reducing the usability of the dredged material further.Clearly, processes and techniques which alter the properties of contaminateddredged material are desirable if they can render the dredged sediment safefor disposal, or better still, suitable for beneficial use. Currently, the Port andHabour Authorities are faced with the problem of having to dredge in order tomaintain navigation channels fortraffic but, additionally in some circumstances,having to deal with the disposal of contaminated dredged material. Thedredging industry has to handle the material, localauthorities have an interestin the disposal of contaminated dredged material on land, and thedevelopment and potential market to sell decontamination technologies lieswith commercial organisations. At present, decontamination technologies,afthough recognised to be an expensive option, are receiving increasingattention. However, they need to be tested on a wide range of contaminantand sediment types so that their potential is realised and appropriatelyemployed.

The perceived problem is the practicality and very high costs of processing thevery large volumes of material associated with dredging, and handling theirhigh water content. A further important issue is whether the importantcontaminants are sufficiently removed. The feasibility and requirement ofdecontamination technologies for contaminated sediments from UK sites withdredging requirements needs to be elucidated.

1.2 ObjectivesThe objectives of this study are:

i) To establish the feasibility of decontaminating dredged material and toidentify the most promising technologies for the purpose.

ii) To define the scale of the problem (quantitative and geographical),

iii) To establish criteria which any prospective technology must satisfy andreview technologies likely to be suitable for dredged material.

iv) Assess the practicality of decontaminating dredged material and write aspecification for the work required to establish the feasibility andusefulness of the most promising technologies.

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trv) To hold a workshop to present initial findings to a target audience and to

obtain the views of industry.

vi) To repod findings of the study in an appropriate publication to promoteindustrial interest.

A workshop titled "Decontamination of Dredged Material" was held by HRWallingford on 23rd January and was well represented by industry, users andresearchers. A report of the workshop is given in Appendix 1. In addition,some of the findings have been published in a paper which was presented atCATS CONGRESS lll held in Ostend in March 1996. A copy of the abstractis given in Appendix 3.

1.3 Report structureThe remainder of this report is in five chapters. Chapter 2 addresses the scaleof the situation as regards dredged material contamination in the UK Thecriteria of importance for a successful decontamination technology arepresented in Chapter 3. Chapter 4 gives a review of the decontaminationtechnologies. For each type of technology the following information is given:basic principle, methods or processes under demonstration, environmentalimplications, estimated costs. Overall conclusions arising from this study arepresented in Chapter 5 and recommendations for further study are detailed inChapter 6.

The report finishes with a reference list for the literature cited throughout thetext and three appendices outlining the HR Workshop, abstracts and the CATSlll Congress.

2 The scale of the problem-quantitative andgeographical

2.1 Dredged material contamination in the UKDredging is a fundamental and critical activity in fluvial and estuarine/ coastalareas. Large quantities of dredged material are generated in the UK everyyear through the essential dredging of navigation channels in ports andharbours and in estuaries of navigable rivers. The majority of dredged material(approximately 40,000,000 tonnes per annum) is disposed of to sea, whileapproximately 1,000,000 tonnes is disposed of to land per annum (MAFF,1ee3).

Generally, during dredging operations, the large quantities of sedimentscollected are mostly inert in nature. However, in some areas high contaminantsmay exist and a small percentage of dredged material (less than 10%) isreported to be contaminated to the extent that disposal at sea is compromised.A wide suite of contaminants may be expected to be present at any onelocation f rom both historical and contemporary discharges made under licence,and accidentalspillage which have led to the accumulation of contaminants inthe sediments. Contaminants generally recognised to be of concern in aquaticsediments of dredging areas include metals (such as Hg, Pb, Cu, Cd andZn),organobutyl tin (eg tributyltin CfBl), organochlorinated pesticides (OCLs),organophosphorus insecticides (OPs), polychlorinated biphenyls (PCBs),herbicides, oil products, polyaromatic hydrocarbons (PAHs), dioxins andfurans. The majority of these contaminants will be preferentially associatedwith the fines (<63pm) fraction and the organic matter of the sediments.

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trAlthough some release of contaminants will occur on dredging, contaminantswill remain in the dredged material which will need to be disposed.

The London Convention 1972, Waste Assessment Framework is currentlyunder discussion and, once annexed, will result in much closer scrutiny of boththe disposal of waste at sea and the examination of alternative options. Thedisposal of contaminated dredged material is therefore likely to becomeincreasingly problematic and expensive such that methods of decontaminatingmaterial will need to be considered.

2.2 Disposal options and constraints2.2.1 Disposal to seaThe nationalframework on dredged material disposal in the UK involves thecontrol of disposal to sea by MAFF using powers contained in Part ll of theFood and Environmental Protection Act 1985 (FEPA), now modified under theEnvironmental Protection Bill. There are no statutory limits regarding levels ofcontaminants, however, under the principles of FEPA and the EnvironmentalProtection Bill, regard to protecting the marine environment, living resourceswhich it supports and human health must be undertaken. In addition regardto the practicalavailability of any alternative disposal methods are to be made.Other legislation which applies is the EC Directive on the Dumping of Wasteat Sea (EC COM, 198S-directive 85/ 373/ EEC).

ln addition the UK is obliged to meet criteria outlined under internationalconventions such as the London and OSPAR (Oslo and Paris combined)Conventions. The London Convention, otherwise known as the prevention ofmarine pollution by dumping of wastes and other matter, has guidelineswhereby the disposal of wastes into the open sea are to be limited andcontrolled.

Other countries have separate systems governing dredged materialmanagement and disposal. The Dutch have more specific guidelines for themanagement and disposal of dredged material and aquatic sediments, with a5 category classification system (0 to lV) according to metallic and organiccontaminant concentrations. Highly contaminated material (Class lV) must bedisposed of to land and contained. Hong Kong have also adopted aclassification system based on metalconcentralions. Canada has a screeningguide for conlaminated sediments. The system in the USA is based more onecotoxicological assays.

Currently, MAFF are setting up action levels (not a set of standards) where thedisposal to sea will be prohibited. These action levels are not anticipated tocome into the public domain for the foreseeable future and decisions are verymuch based on chemical analysis of a suite of contaminants, dictated bynational law and international conventions, and the wide experience andestablished procedures of MAFF statf.

2.2.2 Disposal to landA recent publication gives guidance on the disposalof dredged materialto land(ClRlA, 1995). This report highlights the following:

The position of dredged materialwith regard to disposal on land is not clearlydefined in law, as recently changes in laws regarding waste management haveoccurred.

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trDredged rnaterial for disposal to land is assessed by local authority WasteRegulatory Authorities (WRAs) which are now pad of the recently formedEnvironment Agency.

Legislation of importance includes;Ll Waste Management Licensing Regulations 1994, Sl 1994 No 105612 Environmental Protection Act pail ll-contains a Waste Management

Licensing System which is detailed in the 1994 regulations above.L3 European Community Directives on Waste-(75l442lEEC;

91 /1 56/EEC ; 91 l692lEEC)L4 Controlof Pollution (SpecialWaste) Regulations 1980, Sl 1980 No

1709- overrides exempt waste

Government guidelines include;Gl DoE Environment Circular 11/94-guidance on the concept of wasteG2 Water Resources Act 1991- definition of "inland waters" for

spreading of dredged material on agricuftural land

G3 Agricultural Act 1947- for the meaning of "agriculture"G4 Town and Country Planning Act- if the disposal of dredged material

involves the development of land then planning permission isrequired

G5 EC Environmental Assessment DirectiveGO EC Directive on Landfill has recently been withdrawn, however,

pads of it will continue to be implemented through UK legislation

lmportant points highlighted are:

i) The legislative position of dredged material as a waste is not clearlydefined and activities should not be undertaken without communicationand discussions with lhe relevant bodies ie WRAs, MAFF etc. lt isexpected that the position of dredged materialwillonly become apparentwith time, through the setting of precedent.

ii) That Ll has the phrase "directive wasten, while 12 uses the phrase'controlled waste', but not all 'directive waste" is 'controlled waste*,therefore not subject lo L2.

iiD None of the categodes of waste in L1 refer specifically to dredgedmaterial.

Whether the waste has been "discarded" is of importance, and if it is tobe used in a beneficial way, proof that other materials may have beensought (had the dredged material not existed) will be important. Alsopayment for the material may support applications for exemption fromdisposal licences.

Potential beneficial use options will need to be explored and whereappropriate employed.

Contaminant standards exist which are applicable to the disposal ofdredged material to agricultural land.

Standards for some contaminants exist for landfilU containment eg. PCBconcentrations up to 50ppm are acceptable. This is high compared to

iv)

v)

vi)

vii)

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trconcentrations typically found even in contaminated dredged materialmeaning that few materials will be restricted from landfill sites.

viii) Disposal or use of dredged material on land will also be effected if theland carries a special designation, such as an SSSI (Site of SpecialScientific Interest) or SPA (Special Protection Area) or SAC (Special Areaof Conservation) outlined in the EC Habitats Directive and the EC BirdsDirective.

2.3 Estuarine and coastal areas in the UKAs stated in Section 2.2.1 disposal of dredged material to sea requires alicence from MAFF. Granted licences have recently become open on a publicregister and contain some information on sediment properties and contaminantconcentrations. Historically MAFF have not undertaken sediment particle sizeanalysis, but are now starting to build this information up in a descriptive way(ie 7"sand, "/"silt, "/"clay). The percentage of total solids is given andcontaminant concentrations given include most anthropogenic metals,polychlorinated biphenyls (PCBs) and organochlorine insecticides (eg DDT,dieldrin, lindane). These contaminants are routinely analysed for at sites ofconcem.

ln the USA, dioxins, furans and polyaromatic hydrocarbons are occurring indredged material from ports and harbours and are causing wide concern.These contaminants are currently not routinely analysed for in the UK seadisposal licence system, but may well be in the future and are considered tobe of potential significance.

In UK marine areas it is generally considered that metal contamination is nota widespread problem and organic micro-contaminants such as PCBs, TBT,PAHs and oil products are of greater concern.

The quantities and level of contamination of monitored contaminants indredged materialfrom different estuarine and coastal locations can, therefore,be assessed from licence data where sea disposal is the desired disposalroute. MAFF licence data indicates concentrations and volumes of dredgedmaterial (ie contaminant loads) approved for sea disposal. Refused licenceapplications, or licences granted on condition that some material goes to landdisposal are therefore of great interest with regard to decontaminationtechnologies.

ldentification of sites which already, or which may in the future, presentparticular disposal problems include;

2.3.1 DevonportPreviously, Devonport displayed PCB contamination but the sediments weredredged and disposed of to land. In addition, licence data indicates previouslyhigh concentrations of Cd, with a low level of Hg and Cu enrichment relativeto other dredged material data. Licences to dredge the Naval Wharf displayedthe greatest concentrations for this location.

2.3.2 BlythBlyth is one site in the U.K where investigations into the use ofdecontaminating technologies were researched at pilot scale. At this site, thesediments over a small area of dock were highly contaminated with PCBs(ppm range). The tidal dock was also heavily contaminated with PAHs, Pb, Hg

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trand Cd and heavy petroleum hydrocarbons (TPHs) and Asbestos.Concentrations of PCBs in the silt ranged from approximately 200 pglkg to75,000 trg/kg. However, the final disposal options undertaken wereencapsulation and containment. Decontamination technologies, althoughinvestigated have not yet been employed due to economics and the risksassociated with the unproven status of technologies at plant scale. However,heavily contaminated material is currently being temporarily stored and asolution is being sought.

2.3.3 Falmouthln Falmouth Harbourthere are high TBT concentrations at depth. These arosefrom the past dry dock activities of scraping boat hulls and flushing wastes intothe water. Currently the contaminated area is being left alone, however, in thefuture if dredging occurs the contamination at this site will be an issue,especially because the existing disposal site is located near scallop beds.

A range of metal concentrations are indicated in licences which display verylow/ background concentrations for the majority of metals to high Cu, Pb andZn contamination in some locations. The inner harbour and yacht marina areparticularly contaminated.

2.3.4 PortsmouthContaminated with PAHs. Clean-up is currently under consideration.

2.3.5 East Anglian MarinaThere was a unique situation at this site arising from a very localised incidentof extremely high TBT PCBs, DDT and dieldrin contamination confined to avery small area. The sources of these contaminants, to the extreme levelsdetected, are not known. This materialwas dredged and approximately 330m9of it was placed, at cost, to a commercial landfill site.

Sea disposal licence data from this general area, however, displayed nodistinct metal contamination.

2.3.6 NewportSome estuarine/coastal areas of South Wales have a recognised PCBcontamination problem. PCB contamination arising from industrial activities inthe area. In addition, licence data displayed relatively gross contamination ofCd, Cu, Pb and Zn.

2.3.7 SwanseaCu, and other metals arising from the smelting industry in lower Swansea overthe last century. Also Cu and sulphuric acid from local industrial activities.Licence data shows high sediment concentrations for Cd, Cu, Pb and Zn.

2.3.8 MaryportThe occurrence of trace radioactive contaminates at Maryport marina ispossible. This area has no regular dredging program. However, licence dataindicates sediment enrichment of Pb and Cd.

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tr2.3.9 WhitehavenThis area is contaminated with Cd and Pu2t0. A known source is the phosphateores from local herbicide production.

2.3.10 The Tees EstuaryMetal contamination of the Tees estuary has been previously documented(Delo and Burt, 1991). High metalconcentrations included Cu, Cd, Zn, Pb andHg and these contaminants were monitored at the dredged material disposalground.

2.3.11 The Tyne EstuaryContaminated with metals and consistent requirement for large amounts ofdredging. Metals occur naturally in the environment and marine sedimentsdue to the weathering of rocks and determining metal enrichment due toanthropogenic sources can be difficult. There is no universally recognised orroutinely undertaken procedure for defining metal contamination in sediments.MAFF have used a stretch of this river/estuary to examine different techniquesto determine anthropogenic loads and investigate the best method fromnormalising and defining contamination.

2.4 Inland Waters in the UKIncreasingly UK environmental policy and legislation has been guided atcleaning inland waters and sediments up by reducing inputs. The situation isthat control of point sources (sewage and industrial effluents) of contaminantsin the UK is good and inputs have dropped dramatically since the 1970's/1980's to the extent that surface sediments in fluvial and inland waters arepredominantly "clean". Even though ditfuse (non-point) sources are still ofconcern and difficult to control (eg. atmospheric deposition, run-off from roadsand nutrienVherbicide releases from farming), the need to treat anddecontaminate dredged sediments in UK rivers and canals in the future is notpredicted to be great.

However, there are areas of inland waters where metal contaminants areknown to be of concem and where historic inputs have depositedcontaminated sediments at depth. lf dredged these sediments pose a disposalproblem. Analysis of information as regards a few sites highlighted thefollowing as having a dredging need and contaminant problem.

2.4.1 North West Canal SystemDredged material contaminated with metals (Hg, Pb) are collected from on-going dredging operations and stored in their own disposal ground.Contaminated dredged material is generated from regular maintenancedredging operations, however, here some crude separation occurs simply asa result of the pumping of dredged material from the dredger barges directlyonto the site. At present, the contaminated fines are stored and the coarserfractions washed with the wastewaters being discharged directly back to thecanal.

2.4.2 Birmingham CanalsThe Birmingham canals are an example of where clean-contaminatedsediment separation and washing treatments were employed in a clean-upoperation. Heavily contaminated with metals (particularly Pb, Zn and Cu) andmineral oils, 5 km of canal were dredged for navigational and environmental(remediation dredging) reasons. The removal of approximately 30,000 m3 of

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trsediment was achieved. Of this 5,000 m3 was treated by off-site washing andseparation. Screening, followed by sieving and hydrocycloning wereundertaken with subsequent use or disposal of various fractions of separatedmaterial. Waste water was treated to standards specified by the NRA anddischarged back to the canal. Full process details, dredged material propertiesand contaminant concentrations are reported (Bromhead and Beckwith, 1994).

2.4.3 Nortolk BroadsMercury contamination exists (from historical industrial discharges), and themercury is actively methylated in sediments to methylmercury, anorganometallic contaminant capable of bioaccumulating up the food chain withhealth implications for humans (NRA, 1994). The dredging and disposal ofthese areas is controlled and collected contaminated dredged material iscurrently disposed of to land.

In addition, very high nutrient sediment concentrations exist in the Broadscoupled with a consistent dredging requirement for navigation and recreationalboating purposes. There is concern over the effect of improving water qualityin these areas, the sediments presently act as a nutrient sink. lmproving waterquality could become a problem as the anoxic sediments become oxic andrelease the nutrients.

2.4.4 Weaver CanalExtremely high Hg concentrations have previously been reported.

2.5 Summary of UK ContaminationContaminants of known concern in estuarine and coastalareas in the UK areTBT and PCBs. Metals are not generally causing a problem, with only a fewestuaries showing metal contamination at significant levels.

It is recognised that there are a wide range of organic contaminants currentlynot monitored that may be of potential concern, such as the triazine herbicide,f rgarof 1051, currently being used in CulZn formulations as a replacement forTBT. Analysis for PAHs in dredged material is anticipated to be undertaken inthe future, and these may also be of concern. In addition highly toxic dioxinand furan contaminants are currently not commonly analysed for in dredgedmaterial in the UK Once other contaminants, such as PAHs, dioxins andfurans, are more routinely analysed for, they may also be of concern. Therequirement for decontamination technologies may then become greater.

However, overall the contamination problem in the UK is piece-meal withlocalised 'hot spots" which are often buried at depth and are only of concernwhen capital dredging is considered.

Where such "hot spots" exist, the feasibility of decontaminating dredgedmaterial is of interest. Although the costs are anticipated to be high and thetechnologies are not fully tested on a plant scale, for some sites where localcontaminant "hot spots" occur treatment before disposal to land or sea may bea realoption, and make both environmental and economic sense.

Generally the contaminants of concern in estuarine and coastal areas are thesame for inland waters. Contamination by metals and nutrients are generallyof more frequent and greater concern in these areas.

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trTherefore, currently in the UK decontamination technologies for sedimentshave not been employed to any great extent and are not yet entirely justifiablein terms of volumes of contaminated dredged material. Research is needed sothat the risks, such as unpredictable costs and unknown effectiveness,presently associated with employing decontamination technologies can beproperly addressed.

3 Criteria for a successful decontaminationtechnology

There are many criteria a successful decontamination technology needs tosatisfy which need to be highlighted to aid the development of promisingtechnologies.

3.1 Appropriate technologyA first step, before any choices can be made, will be a sufficient assessmentof dredged material properties and contaminant concentrations so that theproblem which needs to be dealt with is clearly identified. Then the question"What are the appropriate technologies, if any, forthis problem? can be asked.

3.2 Status and efficiency of technology3.2.1 Development/AvailabilityThe availability and development of a technology will need to be known. Themain question to be asked will be "ls the technology commercially available orwhat is its stage of development?"

3.2.2 SuitabilityThe technology will most likely have to remove a range of contaminants(removal or reduction). The percentage removal of contaminants fromsediments willdepend on the contaminant under investigation, the contaminantconcentration of the feed sediment, the operation conditions (temperature,pressure and residence time). Final residual concentrations need to bedetermined. Sediment properties, such as percentage fines (<63pm) andorganic matter will be important since the efficiency will be effected by theadsorption and strength of the bonds.

3.2.3 Practicality (eg process capac$ and contact time)The decontamination technology must be practical. Volumes of dredgedmaterial to be treated are likely to be high, therefore, process capacities willneed to be high and the residence time of the process must agree with theprojects overall timetable.

3.2.4 EffectivenessThe most recognised method for assessing decontamination technologieseffectiveness is by using contaminant concentrations and removal efficiencies.However, it needs to be accepted/ recognised that sediment contaminantconcentrations should not be the only criteria considered and the ecologicalsignificance of dredged material needs to be assessed. lf the correct choicesof decontamination technologies are to be achieved and employed atacceptable costs, the contaminants of importance and at what concentrationsthey are of environmental concern will need to be established.

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NUltimately, the effectiveness will be measured by the ability of thedecontamination technology to alter the material properties sufficiently torender it suitable for beneficial use and sea disposal.

3.3 Costs and benefitsThe technology must be cost-effective compared to alternative options. Asummary of the potential costs and benefits are provided in this section.

3.3.1 Comparing clean-up cosfs with altemative disposaloptions

It will be necessary to compare predicted treatment costs with costs of otheroptions (open water capping, confined disposal facilities) and beneficial useprojects. lt is likely that controlled disposal of highly contaminated dredgedmaterial will involve the greatest costs and this may be a useful marker tocompare against predicted costs of decontamination operations.

The clean-up costs which need to be considered are:

"Pioneering" costs of development

Costs that need to be considered include capital costs of installation,operational costs per tonne, possibly dismantling costs. Running costs includepre-treatment, land area, storage, transpofiation, fuel, additives, posttreatment, final disposal route. Disposal costs of any resulting residues andeffluents.

Costs of monitorinq during and after work.

Cost of dewaterinq contaminated dredqed material. transport and disposal mayalso be a marker for what could be afforded for any decontaminating process.Questions to be asked include; "will it be more cost-effective to transport thecontaminated dredged material to the plant or to have a portable plant andtake it to the contaminated dredged material?".

Overall the costs will depend on the technology, contaminant load reductionrequired, water content and operational conditions.

3.3.2 Environmentalcosts/benefitsEnvironmental costs and benefits are typically more ditficult to assess.However, they include:

Environmental costs involve the transfer of contaminants to other matrices (air,water) and the generation of other waste matedal with potentially acute levelsof contaminants. There will be costs associated with the transfer ofcontaminants to other matrices

Environmental benefits are a solution to the problem, some technologiesreduce contaminant loads permanently and beneficial use of the dredgedmaterial may be possible.

The environmental benefits will be case specific and will need to bedemonstrated. The solution to the immediate problem can be measured interms of an improved water/ marine environment, or the beneficial use of

10 sR 464 16i/07/96

trmaterial. For example, some technologies reduce contaminant loads and,therefore, remove them permanently from the environment.

lf decontamination technologies are to become a recognised option, theirenvironmental advantages over other disposal options (eg. containment) needto be proven.

3.3.3 Changing legislation and emerging regulatory systemDecontamination technologies will have to treat dredged material such thatlegislative requirements, disposal options and beneficial use criteria are allmet.

In addition, an unknown and legislatively undefined situation is "what disposaloptions will be open to the treated dredged material under legislation? (willthey be considered as industrial waste, ie mine tailings)"

3.3.4 Acceptability and public perceptionPublic intervention is playing an increasing role in decision making anddredging activities are no exception. Dredged material needs to be seen asa resource not as a waste and the products will have to be acceptable andmarketable.

Environmental acceptability and public perception are increasingly important.The location of decontamination plants at some sites may be unacceptable tothe public (the NIMBY-NoI In My Backyard syndrome). The transfer ofcontaminants into other environmental matrices during the clean-up processwill be significant since controls will exist under legislation. Air emissions arecontrolled for certain contaminants. ln addition, in removing the contaminantsfrom the dredged material an effluent or waste cake may be generated andneed to be dealt with. Process water must meet standards for effluent qualitydischarged into watercourses or the sewage network.

Therefore, an unacceptable loss of contaminants must be prevented. lt is notacceptable that techniques create greater risks to environmental media thanany other handling/ disposal options of the contaminated dredged material.

4 Review of technologies

4.1 Definition of treatment for this studyThere are numerous methods of treatment of contaminated sediments of whichdecontamination technologies are only a part. Treatment processes includeremediation, in-situ treatment, containment, sediment washing, separationtechniques and decontamination technologies. Confined disposal(containment) facilities are a logical preparatory step for treatment processesor for storage prior to beneficial use. The suitability of a site for large areas ofcontrolled storage will depend on the space available and the soil type.Storage, prior to treatment is occurring at the Marathon Battery Superfund sitein New York and New Bedford Harbour Superfund Hot Spot in Massachusetts.However, the decontamination of sediments specifically are the treatmentprocesses to be critically reviewed in this study and they are very much anemerging technology. Pre- or post- treatment methods that form an integralpart of some of these decontamination methods will also be addressed.

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trCurrent technologies are often under utilised or are still being developed.Therefore the availability of technologies, likely f uture development, practicality,effectiveness and cost of technologies need reviewing before they can beestablished as viable options. Sediment decontamination technologies are verymuch an emerging technology and there is a general absence of information.

4.2 lnternational situation on decontaminationtechnologies

It is recognised that some other countries have more experience in this fieldthen the U.K. Research or demonstration programmes focusing on treatmenthave been established in the U.S.A., Canada, the Netherlands, Germany,Belgium and Japan. Envi ronment Canada's Contaminated Sediment TreatmentTechnology Program (CSTTP), Quebec Development and Demonstration ofSite Remediation Technologies program (DESRT) and the U.S. EnvironmentalProtection Agency's (USEPA) Assessment and Remediation of ContaminatedSediments (ARCS) program are both concerned with problems of the GreatLakes. In addition, sediment decontamination demonstrations forcontaminated sediment from the New YorU New Jersey Harbour are reported(Tetra Tech lnc.and Averett (1994); Averett et al. (1994); Garbaciak, (1994);Garbaciak et a/., (1993)). Additional information and experience of treatmenttechnologies is available from the USEPA's Superfund lnnovative TechnologyEvaluation (SITE) Program and the site specific investigations. TheDevelopment Program Treatment Processes (DPTP) in the Netherlands is alsoactively investigating treatment technologies for sediments and has beenrunning for several years. The Netherlands organisation for applied ScientificResearch (TNO) have been carrying out research programmes since the1980's.

Processes have mostly been evaluated on a laboratory scale and until recentlylittle progress had been made toward field demonstrations of sedimenttreatment. In the USA treatment at production scale is completed or underwayat three Superfund sites; Waukegan Harlcour, Boyou Bonfouca and MarathonBattery. Full scale treatment in Europe has been primarily particle separationtechnologies (discussed in Section 4.3.1), although a number of innovativetreatment technology demonstrations are scheduled to begin shortly (Schoteland Rienks, 1993).

Reviews of technologies include van Germerl et al. (1994), St LawrenceCentre (1993) and PIANC (1995).

4.3 Review of decontamination technologies

4.3.1 BackgroundThis section covers decontamination technologies reported in the literature.The cohesive nature of some dredged material and potential for such materialto have high levels of associated contaminants reduce its usability. There areseveral potential ways to decontaminate dredged material, all costly, and allneeding further research. At present the treatment of contaminated sedimentsexists on a laboratory or pilot scale and few operate on a large scale. Most arelarge scale hydrocyclones that separate sands from silts. The effective andtreatment of sediments contaminated with a wide array of chemicalspecies isnot yet available. Such sediments would involve the use of a range oftreatment technologies (treatment trains).

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trTherefore, there is no'cure-all" treatment. The treatment will depend on thecontaminant species present in the dredged material which require removaland the properties of the dredged material itself, including the water content.No two sites are the same. lt is likely that additional and specialised storageareas may be required as an integral part of the treatment process. In theNetherlands contaminated dredged material from the Port of Rotterdam isgraded and is presently being stored in a large lake (the Slufter) where trialsfor treatment and beneficial uses are being conducted. The most heavilycontaminated material is placed at a lined site called the "Parrots Beak". Bothof these sites are shown in Plate 1.

Assessments of the costs of technologies have been undertaken in otherstudies. However, large uncertainties exist as costs have been extrapolatedfrom pilot scale to full scale. ln addition, the costs will depend on thecontaminant to be treated, the quantity of material and the dredged materialproperties. Typically, the costs of decontamination operations are repoded tobe an order of magnitude greater than costs of sediment disposal (Keillor,1993; Garbaciak, 1994). lt is recognised that if costs can not be reduced, analternative would be to find environmental benefits that justify these costs.

Treatment technologies for contaminated fractions being currently examinedare outlined in Figure 1, where other factors related to the decontaminationoperation as a whole are also displayed.

Treatment technologies have primarily stemmed from innovative technologiesfrom the hazardous waste/ mineral processing fields. While there have beena number of remediation technologies developed for the treatment of soils,there is a general absence of experience on how these technologies wouldperform with sediments.

Clearly the treatment will depend on the contaminant species present in thedredged material which require removal and the properties of the dredgedmaterial. However, no two sites are the same either in the contaminantspresent or in the potential for contaminating adjacent environments. Thisreview deals with the treatment processes both individually and, whereinformation is available, an assessment of individualcontaminant groups, seeFigure 2. Contaminanls assessed will be those outlined in Chapter 2 as beinga current problem within UK sites and contaminants anticipated to be ofconcem in the foreseeable future.

4.3.2 Mechanical separationPrincipally, the techniques separate the fine fraction, where contaminants(especially metals) are generally concentrated, from the coarser fractions.Suitability will depend on the sediments propefiies. Their importance lies intheir ability to reduce total volumes of contaminated material. This means thattransport and storage coats are reduced. In addition, by concentratingcontaminants into smaller volumes other decontamination technologies can beused more cost effectively.

Mechanical methods include separation basins, hydrocyclones, flotation,sieving, sediment washing and dewatedng. These methods are typically pre-or post-treatment steps and are mostly proven technologies for sediments.

Seoaration basins This is a well established method which separates coarsematerial from fines by flushing with water jets, for example, and is applied on

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tra large scale (Diebel and Zwakhals, 1993). This is relatively inexpensivetechnique, and with successful marketing, it may be possible to cover processcosts by the sale of sand.

Hvdrocvclones A hydrocyclone separates the sediment into sand particles and,fines and organic material. Due to the differences in sorption properties ofthese two fractions, the contaminants are generally concentrated in the finefraction, while the sand is relatively clean. The removal efficiency ofcontaminants will be site specific and will depend on the contaminantdistribution within the sediments. Where the dredged material is a >60% sandand the contaminants (such as metals) are predominantly in the fines, thisphysical separation method is well proven. lts use is increasing especially inthe Netherlands and Germany.

An operational hydrocyclone is shown in Plate 1 where the contaminateddredged sediments from the Amsterdam Canals are being separated.

The efficiency of hydrocycloning is optimised by estimating the contaminantfraction and setting the separation factors accordingly. For the hydrocyclonemethod separation becomes increasingly poor for small particle sizes. Thefower fimit of separation is generally 1Opm (van Gemert et a1.,1994).

Current examples of large scale hydrocycloning techniques which separate thesand fraction from the silts and clays in collected sandy dredged materialinclude;

. Francop, Hamburg, GermanyBoskalis Dolman bv environmentalworks (Mitra ll) in Germany separatethe sand from suitable (reasonably high sand content) materialwhich canthen be used. The dredged material is fed into the installation in dryform. The coarse particles are screened off and washed clean. Theremaining dredged material is then turned into a slurry and, viahydrocyclones and sieving, the clean sand is separated from the silt. Theprocess is efficient tor sandy dredged material. The separated sandcomplies with quality criteria for unlimited general purpose use. Thecontaminated silt fraction is processed separately and dewatered to forma firm filter cake. The plant has a capacity of 400 tonnes of dredgedmaterial per hour, with at least 1,000,000 m3 of dredged sandy materialrequiring processing over a 4 year period.

. (Elbe Estuary) Hamburg, GermanyMETHA (Mlchanical freatment of llArbour sediments), is a large scaleseparation and dewatering plant for the treatment of contaminatedsediments from the Elbe estuary. The separated coarse grained sandfraction was found to have very low levels of contaminants and is reused,while the fine grained silt fraction is contaminated and mechanicallydewatered and stockpiled on land at a contained disposal site meetingspecial environmental requirements lor the Hamburg area. The plant isconstructed to receive contaminated dredged material at a rate of2,000,000 m3 per year (Detzner, 1993; 1995). In practice the throughputof the solids fraction amounts to 600,000 tonnes per year, correspondingto 1.2 to 1.4 million m3 per year (in situ) with 50% (by weight of the solidhaving grain size of <63pm (Kothe, 1995).

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tr. Other examples where hydrocyclone separation of contaminated

sediments has been, or is currently employed, include Ghent (Belgium),Amsterdam Canals (The Netherlands-see Plate 2)) and BirminghamCanals (UK).

Flotation Principally, particles are separated from the bulk liquid on the basisof differences in their physical and chemical properties. The applicability offlotation technologies to a wide range of dredged material types is uncertainand will clearly depend on water content. lt is successfully used for theseparation of oil and metal sulphides after flocculation in waste waters.Process capacity is reported to be 500 mt h-t lvan Germert et a1.,1994).

Sievinq A simple method frequently employed before hydrocycloning toremove large objects.

Sediment washinq Sediment washing techniques are incorporated intoseparation methods, such as hydrocyclones. Contaminants are concentratedinto the silt fraction rather than destroyed during the sediment washingprocess. The volume of contaminated material represented by the silts andclays may, therefore, be smaller then the volume of originally contaminatedsediment. The process is relatively inexpensive (Galloway, 1994). In addition,the "clean" sand fraction may be used beneficially.

No contaminants are destroyed during the sediment washing process,however, the volume of contaminated material represented by the silts andclays is smaller then the volume of originally contaminated sediment matrixand the sand fraction may additionally be used beneficially.

Dewaterins This is mostly employed as a post treatment step after the initialseparation, dewatering technologies are mainly undertaken to increase thecohesive nature of sediments and render them easier to handle and moreusable. A reduction in volume of conlaminated sediments can beadvantageous to the overall disposal costs. Generally, the largest problemsexist with fine grained materials as a long period and large areas fordewatering are required. Dewatering can be achieved by dewatering fields(eg. Antwerp and Rotterdam), filter presses and the use of thickeners (whichwill increase treatment costs). lf the material is highly contarninated, problemscan occur due to the uncontrolled oxidation of the material during dewatering(particularly in fields). There is subsequently potential for contaminant leakageand in the production of effluents which may need further treatment. Thecapacity of dewatering appliances are reported to be limiting (s0 m3h-1) (vanGemert et a1.,19941.

Maqnetic separation The use of large magnets to remove magnetic materialis extensively employed for contaminated soil remediation.

4.3.3 Physico-chemicalA wide range of physico-chemical technologies exist which will remove orreduce contaminant loads from the sediment matrix. Contaminated dredgedmaterials commonly display a wide range of contaminants. The situation iscomplex and the removal of metals is fundamentally different to the removalof organic contaminants.

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trExtraction techniques Extraction techniques involve the removal ofcontaminants from the solid matrix using the chemical and physical propertiesof a particular solvent or solvents. This technique does not destroycontaminants but concentrates them into a reduced volume and transfers theminto an aqueous phase.

Acid extraction. Chemical treatments to remove metals involvingacid/ alkaline leaching in a series of stages have been investigated(Muller, 1993). This method can remove heavy metals to belowDutch standards, however, the matrix of the material is destroyedwith no usable products (Stokman and Bruggeman, 1995). lnaddition, the removal of Cd is not always sufficient by this technique(Schotel and Rienks, 1993). The extent of removal depends on theacid mixtures used. However, this treatment method is economicallylimited due to the quantities of acid and lime required. Also, thereis unceilainty as to whether undesirable compounds are formedwhen organic matter is present. Aeration prior to acidification aidsthe process but will increase costs. Acid extractions which havebeen investigated in the Netherlands include hydrochloric acid,biochemically produced sulphuric acid and citric acid.

Complexation extraction; This procedure showed great promise atlaboratory scale, however, due to regeneration difficulties andtechnical complications the use of this technology at plant scale ispredicted to be limited (Stokman and Bruggeman, 1995).

A favoured method emerging in the USA is the solvent extractiontechnology, B.E.S.T. (Basic Extractive Sludge Treatment) Process.It is reported for bench and pilot scale and has had limited full scaleapplication (Garbaciak, 1994). This method involves the strippingand removal of organic contaminants from a solid or liquid matrixusing the chemical and physical properties of a particular solvent orsolvents.

Supercritical fluid extraction; Laboratory scale tests are underinvestigation whereby supercritical fluid extraction (SFE) andsupercriticalwater oxidation (SCWO) are being integrated so thatheavy metal extraction and oxidation of organic components can beachieved in a combined unit operation. this is not demonstrated atfull scale for dredged material, however, SFE is a proven technologyfor certain industrial processes.

The B.E.S.T. extraction techniques seems to be reported as the mostappropriate technique for contaminated dredged material. However,extraction techniques are not likely to have a large scale application inthe future as there seem to be a large number of more advancedcompeting technologies (microbiological, mechanical and thermal).

lmmobilisation techniques This method employs the reverse principle toextraction, whereby here the material is chemically treated or fixed so thatcontaminants are associated with the solids such that they are immobile.Solids will then be either more usable or less of a problem for disposal.Examples include in-situ solidification, which is probably of limited use due tothe large quantities of dredged material involved, the methods inability to

a)

b)

c)

d)

1 6 sR 464 16'/07/96

trconclusively remove or destroy contaminants in the long term (>5 to 10 years)and risk that it will eventually impact on bottom organisms.

Wet air oxidation This is a chemical oxidation process, which uses elevatedtemperature and pressure to oxidise organic constituents present in a liquid orslurried solid waste stream. No reports of its application at pilot scale havebeen found, however, laboratory experiments have been extended to a semi-practical scale. In theory, under high temperature and pressure, organiccontaminants oxidise down to carbon dioxide and water, but in practice theactual composition depends on the material to be treated, pressure,temperature, availability of oxygen and the process duration. Degradation oforganic compounds and reduction of contaminant loads is therefore expected,but may be incomplete.

Indeed, wet air oxidation has been shown not to be effective at destroyingPCBs but it was, however, more effective at PAHs (Garbaciak, 1994).Application of this technology is established for municipal waste watertreatment and sewage sludges. However, taking into account the wet natureof the process it has some preliminary advantages for dredged material as aninitial dewatering pretreatment step is not required and it is reported to beapplicable to slurries (eg from hydrocycloning) without dewatering. Thepredicted limited capacity of plant may reduce its usefulness for dredgedmaterial.

Base Catalvsed Decomposition (BCD) The use of base catalyseddecontamination of sediments from New Yorl</New Jersey Harbour, wherenumerous contaminants occur in sediments and concentrations rank amongthe highest in the USA has been reported (Stern et a1.,1994). Assessed ona bench scale, this method proved to be fairly effective for destroying PCBs,chlorinated hydrocarbons, chlorinated pesticides, and dioxins. The method isreported to have strong capability of removing PAHs. The metal Hg is alsoremoved but not other metals.

lon exchanqe Technologies under consideration for the removal of metalsinclude the use of flocculants to promote sedimentation. However, theselectivity of the tested resins in this study for ditferent metals was roughly ofthe same order and metals such as Ca took up a large percentage of theexchange capacity due to it being present in far greater concentrations.Consequently large amounts of resin would be required to achieve the desiredreductions of toxic metals, such as Cd and Hg, which are typically present atlower concentrations greatly limiting the effectiveness of this technology.

Technologies employing selective cation exchange, through existing complexforming ion exchangers, may be applicable to dredged material and would bemainly used for metal reduction (van Hoeck et a/., 1983). Alum and Ferriccoagulants are considered to be unacceptable due to the high dosagesrequired, while synthetic polymers are thought to have potential. However,techniques need to be selective with respect to heavy metals, preferably atdredged material pH levels (to keep costs, such as pH adjustment, down).Long contact times of up to one week are required making continuousprocessing ditficult.

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tr4.3.4 BiologicalBiological degradation aims to enhance the natural breakdown of organiccontaminants into harmless compounds by micro-organisms and can beundertaken ex situ by land farming (<60% water content) or using a bioreactor(>70% water content). The breakdown will depend on environmentalconditions (temperature, humidity and nutrients) and in order to optimise theprocess, adequate ventilation and nutrients (N, P, K) at the requiredconcentrations are needed. Toxic metals and other non-biodegradablesubstances will not be effected as they are recalcitrant, however, if present inhigh concentrations (>5000ppb (CEDA, 1994)) they cause problems bydestroying the microbial population. In addition, the processes will have to beoptimised to increase contaminant availability for degradation. The applicationfor sediments typically requires oxygen. This increases costs and causes anengineering problem since such large quantities are involved. Consequently,processing is limited to a maximal layer thickness of 40cm (van Gemert ef a/.,1994). Additional limitations arise from the low speed of the process. Forcefiain contaminants, the finalconcentration is reached within an acceptableperiod (few months). For severely contaminated material it remains relativelyhigh and a period of at least one year is likely.

Technologies for the in-situ implementation of enhanced degradation (aerobicbiodegradation, anaerobic dechlorination) of organic contaminants exist (DeMeyer ef a/., 1993). In addition, in Hamilton Harbour, Toronto (Canada) suchan in-situ project is in operation at the time of writing. However, generally, in-situ technologies are more likely to have a use in inland waters and notestuarine/ coastal areas due to greater variability in conditions and increasedturbulence/ sediment mixing.

Additional limitations arise from the low speed of the process; for certaincontaminants, the final concentration reached within an acceptable period (fewmonths) for severely contaminated material remains relatively high and forpurification purposes a period of at least 1 year will have to be reckoned on.The application for sediments, which are primarily anoxic requires oxygenincreasing costs and causing an engineering problem for large quantities'Consequently processing is estimated to be limited to a maximal layerthickness of 40cm (van Gemert et a1.,1994).

Technologies lor the in-situ implementation of enhanced degradation (aerobicbiodegradation, anaerobic dechlorination) of organic contaminants exist.However, they may have a more likely use in inland waters and'not estuarine/coastal areas due to greater variability in conditions and increased turbulence/sediment mixing.

4.3.5 ThermalTypically dewatering and drying is required prior to thermaltreatment. Thermaltreatment can be applied at various temperatures such as to remove, destroyor immobilise contaminants. lf thermaltreatment is to be a realistic large scaleoption for contaminated sediment treatment, then cheap heat sources will berequired.

Thermal desorption Thermal desorption is the application of heat to volatiliseand remove the organic contaminants present in the solid matrix. Thistechnology condenses the volatilised contaminants and collects them as anoily residue of substantially less volume than the original sediment mass.Therefore no net destruction of the contaminants is achieved by this method.

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trsewageThis method has an established application for hazardous wastes,

sludges and soils.

Garbaciak (1994) undeftook pilot scale studies on sediments with PAHcontamination being of primary concern. Conclusions about the effectivenessof this thermal desorption process were, however, difficult for low contaminantconcentration levels in the feed sediment and confounded by the variationinherent in the analytical techniques for PAHs. More specific details of thistechnology are also given in a pilot study of two sites by Kenna et al. (19941.

This method has an established application for hazardous wastes, sludges andsoils. Two technologies are relatively frequently reported lor contaminateddredged material treatment;

a) Remediation Technologies, lnc (RETEC)Garbaciak (1994) undertook pilot scale studies on sediments with PAHcontamination being of primary concern. Conclusions about theeffectiveness of this thermal desorption process were, however, difficultfor low contaminant concentration levels in the feed sediment andconfounded by the variation inherent in the analytical techniques forPAHs. More specific details of this technology are given in pilot study oftwo site by Kenna ef a/. (1994).

b) Soil Tech- Anaerobic Thermal Process (ATP/ Taciuk Process

Incineration Rotary kiln incineration is tested and has a relatively shortprocess time compared to physico-chemical and biological technologies.Operational conditions will vary depending on the target contaminant tobe treated. High temperature (approximately 1200'C) and pressureincineration has demonstrated highly efficient contaminant removal evenfor PCBs and dioxins and is a technical option. This technology iscommercially available, but at high costs (Stern et a1.,1994). In addition,concern about the concentration of metals in the waste ash has beenexpressed. lt is only practical if sutficient organic matter is present andthe contaminants are organic, otherwise the ash willcontain most of themetals and require controlled disposal. The produced gases may needto be recombusted and a gas washer is required to prevent undesirableemissions occur to the atmosphere. However, the incinerationtechnology is progressing at a rapid rate and may become moreeconomic in the future.

Thermal lmmobilisation At 1200"C some organic contaminants are completelyincinerated, whereas non volatile metals are immobilised in the sinteredproduct. An artificial product results which can be used in concrete or asphalt.At higher temperatures (1400'C) , smelting occurs where a liquid melt isproduced. A variety of products can be achieved by controlling its rate ofcooling. Under oxidised conditions a large proportion of the metals remainsin the formed product, but despite this, a thorough flue gas treatment is stillrequired. Such treatment processes have been successfully demonstrated andtheoretically otfer an option for sediments contaminated with a cocktail ofcontaminants or residues from separation processes such as hydrocycloning.However, obstacles to its successful application include the low scaleacceptance of the products and the uncertainty with respect to environmenlalhealth aspects (Vellinga, 1995). In addition, it is an expensive technology.

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trClearly the effectiveness of decontamination technologies with respect toindividual contaminants is of key interest. The suitability of promisingtechnologies for individual contaminant types is presented in Figure 2. lt ishowever, dependant on sediment properties, operational conditions and thepresence of other contaminant groups.

4.3.6 Cosfs of sediment decontamination technologiesThe cost of sediment decontamination will depend on the quantity andproperties of material to be treated (notably water content), the contaminantto be removed and level of removal required and the decontaminationtechnology employed. Costs for full scale application of decontaminatingdredged material are largely uncertain and estimates in the literature arebased on extrapolation from bench or pilot scale. Therefore, costs reportedare indicators only and caution is required in using them. Costs reported aregenerally in US $ and are reported as $ per unit volume or weight. To convertbetween weight and volume, knowledge of the density of the dredged materialis required. As the quantity of materialto be treated increases, generally, thecost per unit weighV volume decreases.

Costs US $per tonne f/m'(wet weight)

Mechanical

Separation

Sediment washing

Physico-chemical

Extraction

Wet air oxidation, basecatalysed decomposition

Biological

Microbial degradation

ThermalThermal desorption

lmmobilisation

lncineration

$70-257

$33-158

Exchange rate $1.55:fBulk density 12O0kg/m3

$s-++

$28

$40-268

$34-945

$39-181

85-35

t25

f30-210

c30-735

f30-140

855-200

e30-125

e1000-2000

Conversion:

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tr

1 .

For example, costs of sediment washing have been quoted to be $258/cy for10,000 cy and $4elcy for 100,000 cy (Garbaciak, 1994). Clearly, there is asubstantial difference in costs here. However, other technhues such asextraction (B.E.S.T.) and therrnal treatment do not display such greatreductions in cost as the quantity of materialto be treated increases.

B.E.S.T. is reported as costing $lZllcy for 25,000cy and $139/cy for100,000cy. While thermal desorption (RETEC process) is repoded as costing$535/cy for 10,000cy and $350/cy for 100,000cy (Garbaciak, 1994).

A good summary of estimated ranges of costs per metric tonne is given byGalloway (1992). A summary of these costs is given on page 20 andapproximately converted into 9m3.

Other estimates repoil decontamination costs to range from $5 to $300 percubic yard or $6 to $200 per dry ton (St. Lawrence Centre, 1993).

lf costs are compared using volume of in-silu sediment treatment, treatmentcosts (biological, extraction and immobilisation) range from $30 to $120 perm3. Dredging and hydrocyclone separation range from $2 to $15 and $2 to$120 per m3 of in-situ sediment respectively (van Dillen and Bruggeman,1 ee2).

5 Discussion and Conclusions

The demand for decontamination technologies is largely uncertain. Anassessment of the geographical need (contaminant problems anddredged material propefiies), the requirements under legislation andlicensing systems and alternative options are involved.

The geographical distribution of contaminated sediments in dredgingareas in the U.K are as contaminated "hot spotsu. Decontaminationtechnologies will need to handle large volumes, high water contents andoften mixtures of contaminants. Each site will have its own specificcontaminant problems and will therefore require potentially differentdecontramination technologies. As research on the most suitabledecontramination technologies continues there is a need to have dueregard to the site specific characteristics from where the material iscoming and flexibility in choosing the appropriate technology is required.

For the decontamination of dredged material to be taken on board fully,then large scale, cost-effective technologies are needed to handle themillions of cubic meters of moderately contraminated dredged materialgenerated by large port and harbour activities.

Much experience is being gained recently in Europe, Japan, Canada andUSA with relatively large scale treatment of sediments.

There are several potential ways to decontaminate dredged material,many of which are presently costly and in need of fuilher research. Theireffectiveness needs to be established, their environmental benefitsdemonstrated and the costs more accurately estimated.

5.

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trtheir

7.

Appropriate technologies need further development andeffectiveness for large scale treatment needs to be tested.

Costs will be dependant on the decontamination technologies employed,quantity of materialto be treated, the dredged material properties and thecontaminant(s) to be removed and the cost of storage and transport. Atpresent there are large uncertainties involved with assessing costs forfull scale application.

While containment remains a legal and cheaper alternative, developmentof treatment technologies will continue to make only slow progress.

Public pressure may influence the solution to the problem ofcontaminated dredged material management. Increasingly severestandards are being made due to public pressure and the increasingrecognition of contaminants toxicity's.

Some technologies may be preferred if an overall integrated pollutioncontrol assessment is considered. Technologies, such as BaseCatalysed Decomposition (BCD) are preferred over extraction techniq uesin this respect, as BCD destroys chlorinated organic compounds ratherthan just remove them from the bulk material.

It is generally assumed, but not proven that the biological effect (humanhealth and ecology) of contaminants present in dredged material is onlyfound in the fine fraction. The separation of silt from sand is based onthe observation that contaminates concentrate in this fraction and that theabove assumption holds.

The initial concentration will affect the efficiency of removal, however, thefinal contaminant concentrations in the sediments against environmentallyacceptable levels will be the key factor determining the success of adecontamination technology.

The environmental benefits of treatment may be economically justified forsome of the most contaminated sites with relatively small sedimentvolumes. Appropriate sediment washing of dredged materialcan be costeffective as opposed to direct land filling of wet material. However,refinements to current sediment washing technologies may be required,particularly the loss contaminants to the atmosphere.

Decontamination technologies seem to be applicable either incombination with controlled disposal of residues or as alternatives tocontrolled disposal.

Public perception of dredged material is important and dredged materialneeds to be viewed as a resource rather than a waste to be disposed of.The environmental merits are clear and beneficial use is becoming arecognised option.

There is no "cure-all" method. The end solution is likely to involve acombination of treatment methods (treatment trains) and disposal options.There are many technologies. Some technologies are proven, whileothers have potential but are currently underdeveloped.

8.

9 .

1 0 .

1 1 .

12.

13 .

14.

15 .

1 6 .

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tr17. The lack of legislative initiatives prohibiting disposal of highly

contaminated sediments to land and allowing 'trace' contaminatedsediments to sea presently renders these technologies uneconomicalandhinders their development. Other factors hindering their developmentinclude the uncertainty in costs, especially "pioneering" costs ofdevelopment, the lack of funding, uncertain demand and market. lnaddition, previously land disposal has been a much cheaper option.There are also uncertainties regarding the final disposal/ beneficial useoptions for treated dredged material and public perception of the activitiesand products may be poor.

An integrated approach will be needed to handle contaminated dredgedmaterial, a requirement for storage areas is likely and, in addition, aheavy reliance on disposal to landfill/containment is likely to remain.

The likely increase in legislative pressure preventing the disposal ofcontaminants to sea, constraints on the capacities of landfill site and thecontinuing contamination in developing countries increase the need fordecontamination technologies. The development and research ofdecontamination technologies, however, needs to be seen as less of afinancial risk and their potential demonstrated with costs being outlined.

The export potential of developed decontamination technologies to othercountries is high.

The findings of this study have been presented at a Seminar held at HRWallingford (January 1996) and at the CATS lll Congress (March 1996)which was an international conference covering the treatment of dredgedmaterial specifically. The work has stimulated a lot of interest. Both theHR Seminar and the CATS lll congress are summarised in Appendix 1and Appendix 3 respectively.

6 Suggestions for further study

Increasingly there are cases in the UK where dredged material is contaminatedto the extent at which disposal options are restricted and costly containmentat commercial landfill sites required. In other parts of the world, much greatercontamination occurs and serious problems which can be addressed by theUK exist.

Examples of UK technologies are available in pilot surveys by privatecompanies, frequently using a combination of techniques to deal with thecocktail of contaminants. lt is anticipated that costs of such clean upoperations at full scale are not necessarily prohibitive and can be competitivewhen compared to disposal at special sites on land.

Developing technologies and solutions to the increasingly recognised problemof the management of contaminated dredged material, which the UK canexport abroad may also be of importance as other contaminants becomeincluded on the list of parameters tested in the licensing procedures.

The approach to such a study should be:

1 8 .

19 .

20.

21.

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trSet up a framework to examine the results such that environmental,economic and socialfactors are also considered alongside the technicaland scientific aspects

Investigate the effectiveness and suitability of promising decontaminationtechnologies over a range of sediment types and contaminant mixes bycarrying out tests at bench and pilot plant scale with industrial partners.

ldentify potential markets based on available information

7 Acknowledgements

The assistance of everyone at the CEDA office in Delft, especially Mrs L. VanDam for arranging meetings with relevant organisations and in providing theuse of their literature base is gratefully acknowledged. Additional thanks aredue to Mr J. Jansen from Boskalis Dolman bv and Mr J. Kreeft from theHarbour Department of the Port of Rotterdam for site visits to AmsterdamCanal treatment plant and the Slufter respectively.

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tr8 References

Averett, D.E. and Francingues, N.R. (Jr). (1994) Sediment Remediation: AnInternational Review. Dredging 1994, l, 596-605.

Delo, E.A. and Burt, T.N. (1991). Distribution of heavy metals at a disposalsite f or contaminated estuari ne dredged material. CATS Cong ress, Antwerpen.

Bromhead, J.C. and Beckwith, P. (1994). Environmental Dredging on theBirmingham Canals: Water Quality and Sediment Treatment. J. IWEM, 8, 350-359.

Deibel, l.K. and Zwakhals, J.W. (1993). Separation from Sand out of Sludge.A Large Scale Test, CATSII

Detzner, H.D. (1993). MechanicalTreatment of the Dredged Materialfrom theHamburg Harbour. CATSII

Detzner, H.D. (1995). The Hamburg Project METHA: Large -Scale Separation,Dewatering and reuse of Polluted Sediments. European Water PollutionControl, 5,5,38-42.

De Meyer, Ch.; De Vos, K.; Malherbe, B. and van der Zwaan. (1993).Experiences with in-situ ABR-CIStm Bioremediation of Sediments in Harboursand Waterways. CATSII

Galloway, J.E. and Snitz, F.L. Pilot-Scale Demonstration of Sediment Washing.Dredging 1994, l, 981-990.

Garbaciak, S. (1994) Laboratory and Field Demonstrations of SedimentTechnologies by USEPA's Assessment and Remediation of ContaminatedSediments (ARCS) Program, Dredgings 1994, l, 567-578.

Garbaciak, S. Jr.; Fox, R.;Tuchman, M.; Cowgill, D. and Dennis-Flagler, D.;Yaksich, S., Averett, D. and Timberlake, D. (1993). Laboratory and FieldDemonstrations of Sediment Treatment Technologies by the USEPA'sAssessment and Remediation of Oontaminated Sediments (ARCS) program.cATStl

Keillor, J. Ph. (1993). Obstacles to the Remediation of Contaminated Soils andSediments in North America at Reasonable Cost. CATSII

Kenna, T., Conboy, D.J., Leithner, J., Yaksich, S. and Averett, D. Pilot-ScaleDemonstrations of Thermal Desorption for the Treatment of ContaminatedRiver Sediment. Dredging 1994, 4,474-483.

Kothe, H. F. (1995) Legislative framework and technological improvement forthe management of contaminated dredged material (CDM) in Germany. ln theframework of the Fifth lnternational FZI(TNO Conference on ContaminatedSoil, (30 October-3 November 1995). Maastricht Exhibition and CongressCentre (MECC), Maastricht, the Netherlands.

25 sR 464 16/07196

trMAFF (1993). Monitoring and Surveillance of Non-Radioactive Contaminantsin the Aquatic Environment and Activities Regulating the Disposal of Wastesat Sea, 1991. Aquatic Environment Monitoring Report, Number 36. Ministry ofAgricultural Fisheries and Food. Directorate of Fisheries Research.

Muller, G. (1983). Chemical decontamination: A concept for the final disposalof dredged materials and sludges contaminated by heavy metals. In: HeavyMetals in the Environment International Conference Heidelberg, September1983,948-951.

NRA (1994). Yare Catchment Management Plan Consultation Repoft, lpswich,pp155. National Rivers Authority, Anglian Region.

PIANC (1996) Handling and Treatment of Contaminated Dredged Materialf romPorts and Inland Waterways. Volume l. PIANC Report PTC1|17.

Stern, E.A., Olha, J., Wisemiller, B. and Massa, A.A. Recent Assessment andDecontamination Studies of Contaminated Sediments in the New York/ NewJersey Harbour. Dredgings 1994, l, 458-467.

Srnits, J. (1994). TreatmentTechniques for Dredged Material. Central DredgingAssociation (CEDA) February 1994.

Schotel F.M., and Rienks J., (1993). Chemical Treatment and lmmobilisationof Contaminated Sediment in the Dutch development Programme SedimentTreatment Processes DPTP Phase ll (1992-1996) CATSII

Stokman, G.N.M. and Bruggeman, W.A. (1993). Remediation of ContaminatedSediments Developments in the Netherlands. CATSII

Stokman, G.N.M. and Bruggeman, W.A. (1995). Cleaning of PollutedSediment. European Water Pollution Control, 5, 5, 25-30.

St Lawrence Centre (1993). Screening Guide for Contaminated SedimentTreatment Technologies. By Jean-Rene Michaud, Technology DevelopmentBranch. Cat. No. En 40-450/1993E.

Tetra Tech, Inc., and Averett, D.E. (1994) Options for treatment and Disposalof Contaminated Sediments from New York/ New Jersey Harbor.Miscellaneous paper EL-94-1, US Army Engineer, Waterways ExperimentStation, Vicksburg, MS

van Germert, W.J.Th.; Quakemaat, J. and van Veen, H.J. (1994). Methodsfor the Treatment of Contaminated Dredged Sediments. In: EnvironmentalManagement of Solid Waste; Dredged Material and Mine Tailings. EdSalomons, W and Forstner, U. Springer-Verlag.

van Hoeck, G.L.M.; Gommers, P.J.F.; Overurrater, J.A.S (1989). Removal ofheavy metals from polluted sediments: lon exchange resins a possiblesolution. In: Heavy Metals in the Environment International ConferenceHeidelberg, Spetember 1983, 856-859.

Vellinga, T. (1995). Treatment and Beneficial Use of Contaminated Sediment,Past and Present: Port of Rotterdam Case Study. European Water PollutionControl, 5, 5, 31-37.

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trVolbeda, J.H.; van der Schrieck, G.L.M. (1991) Cleaning the HeavilyContaminated Geulhaven at Rotterdam. CATS Congress

Garbaciak, S. (1994). Laboratory and field demonstrations of sedimenttechnologies by USEPA's assessment and remediation of contaminatedsediments program, Dredgings 1994, l, 567-578.

St Lawrence Centre (1993). Screening guide for contaminated sedimenttreatment technologies. By Jean-Rene Michaud, technology DevelopmentBranch. Cat. No. 40-450/ 1993.

27 sR 464 16&7/96

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Figures

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TMENTTECHNICAL OPTIONS

Separation techniques eg. HydrocycloningSediment washing

Oewatering

Extraction (acid l€aching. complexation extraclion. B. E.S.T.)Chemical immobilisation

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lon exchange

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by micro-organisms

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Figure 1 Decontamination Technologies

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MetalsHg

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acid

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Immobilisation

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Plates

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The Slufter and "Parrots Beak", Rotterdam HarbourPlate 1

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Plate 2 Amsterdam Canal Clean-up using Hydrocyclone

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Appendices

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Appendix 1

Summary report on the Workshop

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trAppendix 1 Summary report on the Work Shop

As specified in the contract a work shop titled "The decontamination ofDredged Material" was held at HR Wallingford to bring together interestedparties and open a discussion forum with industry. A list of participants, theworkshop programme and abstracts of the presentations are presented inAppendix ll. The presentation on decontamination technologies given by HRWallingford reported the initial findings of this report to the target audience andobtained comments from researchers and practitioners on aspects of some ofthe treatment options. A list of speakers and abstracts of the presentationsfollow:

sR 464 16/07/96

THE DECONTAMINATION OF DREDGED MATERIAL

Tuesday 23 January 1996

HR Wallingford Ltd Wallingford, United Kingdom

Synopses

The UK Situation and the Future Role of Decontamination Technologies

Review of Decontamination Technologies

Market and Technology: will they match?

Steve Warren Consultant

Caroline Fletcher HR Wallingford

Martin Kroezen

Heijmans Milieutechniek BV

Decontamination by using Supercritical Dr Mike Butcher and Chris Riley Fluid Technology BHR Group Ltd

Netherlands Development Programme for Treatment Processes for Polluted Sediments (POSW)

Pilot Scale Demonstrations of Decontamination Technologies

Gerard Stokman Rijkswaterstaat

Dudley Gibbs Biolytic Systems Ltd

A Case Study Colin Robson North Blyth - Battleship Wharf Scheme Northumberland County Council

The British Waterways Experience Nick Smith British Waterways

The UK Situation and the Future Role of Decontamination Technologies

Steve Warren, Consultant

EU and UK waste regulations are being framed to reflect the fact that sacrificial disposal is now the last resort. The broad aim of legislation is to encourage the beneficial use of waste components and to avoid risk to health or to flora, fauna and the environment in general from contaminants that may be present in waste. The general result is to increase the cost of disposal.

Waste disposal to landfill, to sea, by incineration or by spreading on land are all governed by different regulations and conventions. EU Member States have stopped sea disposal of industrial wastes and will cease dumping sewage sludge by 31 December 1998 in accordance with the Urban Wastewater Treatment Directive. The disposal of dredged material is covered by the London Convention (1972) which permits the disposal of material containing specified toxic substances providing they are present only in "trace" amounts. Revisions to the Convention now under consideration would extend its scope to cover all dredging operations but a lack of toxicity data has prevented the development of quantitative criteria for contaminants in dredged material which could be used to determine its acceptability for sea disposal.

Spreading on land is now permissible only if there is a definable benefit to the soil and if contaminant levels are such that soil loading does not breach standards. Incineration is only practicable if the material is at least partly combustible and only worthwhile if its bulk is significantly reduced by combustion, which is unlikely to be the case for dredged material.

The classification of wastes and the regulations governing their disposal to landfill are currently being revised in both the EU and the UK. The containment requirements are least for inert wastes, intermediate for non- hazardous wastes and most stringent, and therefore most costly, for special wastes. Schedule 2 of the draft regulations lists sources of waste defined as special by virtue of their origin. It does not include dredged material but wastes not listed in Schedule 2 are defined as special if they are contaminated to the extent that they meet certain criteria, for example if they contain not less than 0.1% of substances defined as very toxic, or not less than 3% of toxic substances or a number of other conditions.

It is likely that only rather heavily contaminated dredged material would be classified as special waste on the basis of risk to human health but the last set of criteria relate to eco-toxicity. For this category the proposed criteria are not quantitative. The mere presence of any of the so-called class 'N' substances, with ecological effects (eg PCBs, TBT), is sufficient for the waste to be classified as special.

European pressure against the marine dumping of contaminated material is not likely to decrease and the cessation of sludge dumping in 1998 will leave dredging spoil in isolation. Whatever the UK view it will be difficult to resist this pressure. The cost of alternative disposal routes will be high (eg the price of disposing of special wastes can range from £40-£75/m3) and

decontamination may look like a cheaper option than it does at present. Even if we start now it will take at least until 2000 to make good our current lack of experience of decontamination technologies.

Review of Decontamination Technologies

Caroline A Fletcher, HR Wallingford

The dredging of navigational channels and waterways in the UK is an economically essential activity. However, contaminated sediments in some of our rivers, estuaries, ports and harbours, canals and marinas mean that the dredged material collected may have restricted disposal options under UK legislation and licensing systems. In addition, the likely increases in legislative pressure preventing the disposal of contaminated sediments to sea may have serious implications to current disposal practices for dredged material. Alternative disposal options and beneficial uses will be increasingly sought for contaminated dredged material.

Currently, the Ports and Harbours Authorities and Inland Waterways are faced with the problem of having to dredge in order to keep navigation channels clear for traffic but, in some circumstances, having to deal with the disposal of contaminated dredged material. The dredging industry have to actually handle the material, MAFF and local authorities have an interest in the disposal of contaminated dredged material, and the development and potential market to sell decontamination technologies lies with the commercial organisations.

Clearly, processes and techniques which alter the properties of contaminated dredged material are desirable if they can render the dredged sediment suitable for disposal, or better still, suitable for beneficial use. At present, decontamination technologies, although recognised to be an expensive option, are receiving increasing attention. However, in reviewing the decontamination technologies factors which need to be considered include:

1 Criteria for a successful decontamination technology 2 The situation in the UK and other countries 3 Current Decontamination Technologies 4 Factors hindering their development

1 Criteria for a successful decontamination technology

There are many criteria a successful decontamination technology needs to satisfy which need to be considered when reviewing decontamination technologies.

Meeting legislative requirements

Appropriate technology, practicality and suitability based on a site by site basis

Status, efficiency, effectiveness and process capacity of technology

Costs1 Benefits

Environmental acceptability and public perception are increasingly important.

Resultant material meets the disposal options1 beneficial use criteria

Basically is the technology available, effective, and is i t economically and environmentally acceptable?

2 The situation in the UK and other countries

It is recognised that presently some other countries have more experience in this field then the UK Research or demonstration programmes focusing on treatment have been established in the USA, Canada, the Netherlands, Germany, Belgium and Japan. For example, the Development Program Treatment Processes (DPTP) in the Netherlands is actively investigating treatment technologies for sediments and has been running for several years. An overview of the research findings from the DPTP programme is being given later at this seminar.

Currently, in the UK there are few examples of research into decontamination technologies for sediments. The majority of dredged material generated in the UK, is inert in nature and disposed of at sea (approximately 40,000,000 tonnes per annum). However, in some areas contaminated sediments exist to the extent that, on dredging, their disposal to sea is compromised, and consequently disposal to land adopted. The actual quantities disposed to land are difficult to quantify.

The contamination of UK estuaries and waterways is generally localised "hot spots" which are often buried at depth and are of concern when dredging operations are considered or required. Where such "hot spots" exist, the feasibility of decontaminating dredged material is of interest. In UK marine areas it is generally considered that metal contamination is not a widespread problem and organic micro-contaminants such as PCBs, TBT, PAHs and oil products are of greater concern. There are, however, some examples of inland waterways where metal contaminants are of concern.

One estuarine site in the UK where investigations into the use of decontaminating technologies are currently under review is Blyth, Northumbria. Lessons learnt through pilot scale studies at this site will be given at this seminar.

3 Current decontamination technologies

There are numerous potential methods of treatment for contaminated sediments both in-situ and ex-situ of which decontamination technologies are only a part. At present most sediment decontamination technologies exist on a laboratory or pilot scale and few operate on a large scale and are, therefore, very much emerging technologies. Generally, there is a lack of information regarding their application with large volumes of contaminated dredged material. Pre- or post- treatment methods form an integral part of some of these decontamination methods and methods such as the large scale separation of silts and sands by hydrocyclones and dewatering techniques have been demonstrated for sediments.

Dredged sediments may have a range of contaminants of concern present. However, there is no "cure-all" decontamination technology. The technology1 technologies required will depend on the contaminant species present in the dredged material which require removal and the properties of the dredged material itself, including the water content. No two sites are the same.

Assessments of the costs of technologies have been undertaken in other studies. However, large uncertainties exist as costs have been extrapolated from pilot scale to full scale. In addition, the costs will depend on the contaminant to be treated, the quantity of material and the dredged material properties. Typically, the costs of decontamination operations are reported to be orders of magnitude greater than costs of sediment disposal. The majority of treatment technologies for contaminated fractions currently examined are outlined in Figure 1, where other factors related to the decontamination operation as a whole are also displayed.

Mechanical Principally, the techniques separate the fine fraction, where contaminants (especially metals) are generally concentrated, from the coarser fractions. Their importance lies in their ability to reduce total volumes of contaminated material and concentrate contaminants enabling decontamination technologies to be used more cost effectively.

These mechanical methods are separation techniques; Such techniques include separation basins, hydrocyclones, flotation and sieving. In addition sediment washing and dewatering. These methods are typically pre- or post- treatment steps and are proven technologies for sediments.

Physico-chemical A wide range of physico-chemical technologies exist. Contaminated dredged materials commonly display a wide range of contaminants. The situation is complex and the removal of metals by physico-chemical processes is fundamentally different to the removal of organic contaminants.

Degradation of organic compounds and reduction of contaminant loads by some techniques will occur, but may be incomplete. Not all techniques, however, destroy contaminants but instead concentrate them into a reduced volume and transfer them into an aqueous phase. In addition, the final disposal option of the dredged material may be limited if solvents are used for example.

Biological Biological degradation aims to enhance the natural breakdown of organic contaminants into harmless compounds by micro-organisms. The breakdown will depend on environmental conditions (temperature, humidity and nutrients) and in order to optimise the process, adequate ventilation and nutrients (N,P,K) at the required concentration are needed. Biological treatment is not very successful for all contaminants eg (PCBs, "heavy PAHs"). In addition, metals will not be effected as they are recalcitrant (eg Cd, Cu), however, if present in high enough concentrations metals may cause problems by destroying the microbial population.

Thermal Typically dewatering and drying is required prior to thermal treatment. Thermal treatment can be applied at various temperatures such as to remove, destroy or immobilise contaminants. If thermal treatment is to be a realistic large scale option for contaminated sediment treatment, then cheap heat sources will be required.

4 Factors Hindering the Development of Decontamination Technologies

Uncertain demand1 market for the technologies

Requirement is strongly driven by changing legislation

Costs; the risks involved in taking on "pioneering" costs

Until recently, the much cheaper costs of land disposal prevented development

Uncertainty of final disposal1 beneficial use options for treated sediments

Public perception of products can prevent success

Key Points

Defining the situation The demand for decontamination technologies needs to be clarified based on the geographical need (contaminant problems and dredged material properties) and the requirements under changing legislation and licensing systems.

The geographical distribution of contaminated sediments in dredging areas in the UK are as contaminated "hot spots". Each site will have its own specific contaminant problems and will, therefore, require potentially different decontamination technologies.

Large scale, cost-effective decontamination technologies are needed to handle the millions of cubic metres of moderately contaminated dredged material generated by large port and harbour activities and inland waterways.

Decontamination technologies There are several potential ways to decontaminate dredged material many of which are innovative. However, currently most are costly, further research is needed so that their effectiveness for large scale treatment can be established, their environmental benefits demonstrated and the costs more accurately estimated.

Costs will be dependant on the quantity of material to be treated, the dredged material properties and the contaminant(s) to be removed. At the moment there are large uncertainties involved with assessing costs for full scale application.

The initial concentration will affect the efficiency of removal, however, the final contaminant concentrations in the sediments after treatment against "safe" levels will be the key factor determining the success of a decontamination technology.

The environmental benefits of treatment may be economically justified for some of the most contaminated sites with relatively small sediment volumes.

Currently decontamination technologies seem to be applicable either in combination with controlled disposal of residues or as alternatives to controlled disposal.

Public perception needs to be changed so that dredged material is viewed as a resource rather than a waste to be disposed of. The environmental merits are clear and beneficial use is becoming a recognised option.

Are decontamination technologies feasible? Technically some decontamination methods are proven and others have great potential. Existing and innovative technologies are more likely to develop if legislatively driven and if a real future for their requirement, against alternative options, is demonstrated. Further research and development is required, and although in industrially developed countries the handling of contaminated sediments is becoming a decreasing problem as source inputs are controlled, in developing countries, who are even less able to afford clean-up technologies, contamination of navigable waterways is still occurring and decontamination technologies will be needed.

Decontamination by using Supercritical Fluid Technology

Dr Mike Butcher and Chris Riley

BHR Group Limited in conjunction with Leeds University's supercritical fluids group, have been developing a cost-effective solution for the clean, energy- efficient treatment of both the organic and metallic components of contaminated materials in one combined unit operation. By integrating supercritical fluid extraction (SFE) and supercritical water oxidation (SCWO) respectively, it is possible to extract heavy metal components, and to oxidise the remaining organic matter to relatively harmless oxidation products -

namely, carbon dioxide and water. Moreover, it is possible to fuel the processes by harnessing the thermal energy that is generated from the incineration of municipal waste. Also, the recovery of valuable, high-purity heavy metals affords a potential means of capital repayment of the costs that are associated with the design and construction of new plant.

The presentation is divided into four parts: (I) properties and uses of supercritical fluids; (11) SFE; (Ill) SCWO; (IV) combined unit SFE-SCWO operation, fuelled by waste thermal energy.

A supercritical fluid (SCF) is a substance that above a certain critical temperature will not condense, but exists only as a single fluid. However, for the purpose of decontamination, supercritical carbon dioxide and supercritical water are of particular interest as they are widely available, cheap and harmless to the environment in comparison with the organic solvents that are used in conventional processes. For carbon dioxide, the critical temperature is only 31 "C. Moreover, the physical properties of SCFs, which are intermediate between those of a gas and a liquid, may be manipulated usefully by control of pressure and temperature.

For example, solvation power increases as the density of a SCF increases, thereby enabling SFE to be made selective for different solutes such as heavy metals. Subsequently, metals may be selectively precipitated by decreasing the density of the SCF, thus leading to high purity products with a market value. The high values of diffusion coefficients in SCFs make SFE processes generally faster relative to conventional extraction, and low viscosities give better penetration of the fluid into the matrices of the solid material. In short, SFE may be viewed as an intensified extraction process, that is clean and economically feasible. Moreover, SFE is a proven technology for the extraction of complex organics: on an industrial scale, it is used for the decaffeination of green coffee beans'*2, extraction of different fractions from hops3 and spices as well as for the extraction of essential oils4. Process-scale SFE is becoming widely used in Germanys and Japan, and hydrothermal processing of metallic complexes in the ceramics industry is well understood.

In order to explore the potential benefits of SFE's, BHR Group and Leeds University are linking the physical chemistry of SFE to the design of process- scale equipment by encoding the kinetics into computational fluid dynamics (CFD). This approach is generic in nature, and therefore also applicable to the treatment of industrial, municipal and dredged wastes.

Water above its critical temperature and pressure of 374 'C and 221 bar is able to dissolve many compounds, and can be used in the SFE of heavy metals and other contaminants from dredged waste. It may also prove possible to use SCWO in parallel or simultaneously (depending on reactionlextraction temperatures), to convert the organic matter, by reaction with dissolved molecular oxygen, to carbon dioxide and water=' - as in the MODEC process6. In contrast to conventional incineration, the production of NO, and SO, is avoided, and complex scrubbing systems are not required. Instead, compounds containing nitrogen, sulphur and halogens produce relatively harmless nitrogen, and sulphate and halide ions respectively7. An additional benefit is that oxidation reactions are highly exothermic: therefore in SCWO the temperature can rise to ca. 6000 "C. And if the organic component is present in concentrations above 20%, the process can be run autothermically (i.e. self-sustaining in reaction temperat~re)~. The thermal energy may also be recycled to the inlet of the SCWO reactor, or used for the generation of electricity6.

The fundamental reaction kinetics of SCWO of different substances are being widely studied7-1°. At Leeds University, kinetic studies of the SCWO of model compounds such as phenol are being studied in tubular, plug flow reactors". As a result, BHR Group will be able to combine the physical chemistry of the SCWO process with the fundamental fluid dynamics of process-scale oxidation reactors.

As EEC legislation comes into force, the trend for the disposal of municipal waste is towards incineration, which leads to the production of Fly and Grate ashes with a high heavy metal content. A significant number of large urban conurbations are located near harbours with dredging problems, and in an innovative approach to the decontamination of dredged sludge and ash, it is proposed to couple incineration with SFE and a SCWO reactor. Heat for the initiation of the oxidation reaction would come from the incinerator. Upon the attainment of an initial reaction temperature of ca. 1000 "C, and given sufficient organic matter, the process would become autothermic, and should provide high-grade thermal energy that will be recycled. BHR Group are currently developing the outlines of such a project.

REFERENCES

King, M.B. and Bott, T,R. (eds), "Extraction of natural products using near-critical solvents", Blackie, Glasgow (1993) Leyers, W.E. et.al., "The Economics of Supercritical Coffee Decaffeination", Proc. Int. Symp. on Supercritical Fluids, p.261 (1991) Moyler, D.A., in "Distilled Beverage Flavora - Recent Developments", Piggott, .l.R., Patterson, A. (Eds), Ellis Horwood, Chichester, p.319 (1989) McHugh, M.A. and Krukonis, V.J., "Supercritical Fluid Processing: Principles and Practices", Butterworths, Stoneham, MA (1986) Woolf, G., "Germans give sludge treatment a helping hand", The Chemical Engineer, 30 June (1994), p.24 Clayton, R., "Supercritical Water Oxidation Process", Industrial Waste Management- Sludge Treatment & Disposal, August (1944), p.15 Savage, P.E. et. al., "Reactions at Supercritical Conditions: Applications and Fundamentals", AlChE J., fi (7), p.1723, 1995 Gopalan, S. and Savage, P.E., "A Reaction Network for Phenol Oxidation in Supercritical Water", AlChE J., fi (8), p.1864 (1995)

9. Brock, E.E. and Savage, P.E., "Detailed Chemical Kinetic Model for Supercritical Water Oxidation of C, and H,", AlChE J., 41 (8), p.1874 (1 995)

10. Boock, L.T. and Klein, M.T., "Experimental and Mechanistic Modelling of the Oxidation of Simple Mixtures in Near-Critical Water", Ind. Eng. Chem. Res. 1994,33, p.2554

1 1 . Dr A A Clifford, Supercritical Fluids Group, Leeds University, personal communication

Netherlands Development Programme for Treatment Processes for Polluted Sediments (POSW)

Gerard Stokman, Rijkswaterstaat

Most sediments in the Netherlands are polluted with heavy metals and organic compounds. Approximately 10 million cubic metres of polluted sediments are removed annually for maintenance of harbours and waterways. In addition remediation is required for about 100 million cubic metres of sediment, mainly deposited in the years 1960 - 1980. The sediment mostly contains various mixtures of oil, heavy metals, PAH's and organochlorine compounds in levels that imply a potential risk for human health and the environment. Isolation or in-situ treatment of the polluted sediment has not yet proved to be applicable. Therefore confined disposal or ex-situ treatment of dredged material are the two main options in dealing with this huge problem in the Netherlands. Since storage does not seem the best solution in the long term, because of the possible penetration of pollutants in surface and ground water and of the NlMBY (not in my backyard) - effect, it is better to clean the polluted sludge so that it can do service as sediment or be useful in civil engineering. Further more treatment reduces the dispersal of contaminants in the environment.

The Dutch policy on contaminated dredge material is to treat 20% in the year 2000. By this the necessary storage capacity will decrease and the re-use of raw materials will be stimulated. To realize this commitment it is necessary to build and exploit treatment facilities and actual offer dredged material for treatment. For the development of treatment processes a national programme, in Dutch called "Programma Ontwikkleing Saneringsprocessen Waterbodems" (POSW), in English "Development Programme for Treatment Processes for Polluted Sediments", is under execution which aims at environmentally sound technologies for dredging and treatment, and at testing chains of treatment technologies through pilot remediations. In its second stage (1992 - 1997), the build up of the programme follows the logical order:

- site investigation - environmental friendly dredging technologies - classification of the sludge and polishing of fractions - biological or chemical treatment technologies to clean (fractions of) the

dredged material - and finally thermal immobilization as zero waste option for severely

contaminated sludges or residues from separation or chemical treatment.

POSW is currently focussing on a number of operational technologies. The applicability of such technologies as part of an integrated clean up chain has and will be proven in the field, in the framework of a financial and environmental assessment of the entire chain.

The Dutch Development Programme for Treatment Processes (POSW) for polluted sediments showed that determining the extent and composition of pollution is the first essential step in sediment remediation. Accurate site

characterisation, in quantity and quality, optimises the amount of material to be dredged and the choice of treatment technologies to be applied. Effort and funds invested in this part of the process will be earned back later on.

Environmentally sound dredging depends strongly on precise and careful working methods to prevent spillage and dispersal. An adequate positioning system is a prerequisite. Complications with debris can be overcome with a two stroke dredging approach: first a rough stroke, followed by a precise second cleaning stroke. Environmental requirements will become more and more strict, with attention for a high accuracy, a minimal increase of the suspended solids concentration and minimal spillage.

The Dutch policy to recover and use 20% of the dredged material can be realised. Separation of clean sandy fractions is the first essential step, but additional treatment is necessary to realise this commitment.

Flotation of separate fractions has been tested on a semi-practical scale. Remaining contaminants in the sandy fraction can be removed and oil and PAH can be concentrated from fine fractions in a small part of the initial feed.

In addition, biological and chemical treatment technologies offer several options to deal with organic pollutants like oil and PAH. The remaining problem of sediments contaminated by heavy metals or cocktails of pollutants and of residuals from separation can be dealt with by thermal immobilization. Immobilization offers a zero waste option resulting in products like artificial gravel or basalt that can be applied as a secondary raw material.

In the remaining period till the end of POSW-II (December 1996) various promising technologies will be tested in two forthcoming pilot remediations. The instruments that have been developed for assessment of costs and environmental effects will be improved and made available to water management, eg, in manuals.

POSW-II results will be used for policy development as well as for advice on future sediment remediation projects. This will include both preparation and execution of dredging and treatment of polluted sediments as well as the reuse of the treatment products.

The achievements up to now show that the separation of sand from dredged material is applicable at low costs. In addition further polishing of fractions (eg flotation) and biological and chemical remediation will be necessary and available to reach the national aim of 20%. Finally thermal immobilisation offers a zero waste option for contaminated sediments or residuals of treatment technologies.

Pilot Scale Demonstrations of Decontamination Technologies

Dudley Gibbs, Biolytic Systems Ltd

1. Introduction

The silt from the tidal dock area of Blyth Harbour and used in the study is contaminated with Polychlorinated Biphenyls (PCB's), Poly Aromatic Hydrocarbons (PAH's), Lead, Mercury, Cadmium, Heavy Petroleum Hydrocarbons and Asbestos. The concentration of PCB's in the silt ranges from below 200 pg l kilo up to 75,000 pg l kilo dependant on the place of sampling.

The main objectives of the study were as follows:

i) Set up semi-tech scale techniques and procedures for decontaminating silt from the seabed;

i i) Determine the optimal conditions for physical, chemical and microbiological treatment of silt;

iii) Establish a semi-tech scale biological plant and optimise the conditions needed to destroy PCB's, and alkane hydrocarbons in liquid effluents arising from treatment processes;

iv) Investigate the parameters for a process protocol that could be operated at full scale.

1. Outline trial procedures

A semi tech scale unit that could process 2m3 per day of contaminated liquid was constructed and set up on the site together with holding tanks and a screening l fractionating facility which could process 1 m3 silt per day. A series of procedures were then executed to determine necessary parameters as follows:

i) Silt fractionation.

ii) Biological treatment of washings and liquid arisings.

iii) Particle size analysis.

iv) Chemical treatment of silt concentrate

v) Microbiological treatment of silt

Samples were taken at appropriate stages in the processes. Silts were air dried prior to being analysed for the relevant analytes using standard methods and the results reported on a dry weight basis. Supernatant liquids were analysed directly and the results reported on a weight volume basis.

Total petroleum hydrocarbons were determined by Soxhlet extraction and gravimetry. PCB content was determined by the NRA Exeter laboratory using NAMAS approved GC-MS protocols.

1. Results - summary

Biological treatment of PCB's in aqueous phase.

Harbour silt PCB analysis by particle size

PCB analytical results

ngllitre

Fractionation of the silt PCB analytical results yglkg

Fractionation of the silt showed that 83% of the PCB's were combined with the particles in the range 125 -500 microns

Control

28447.2

Influent before treatment

12771.6

1. Conclusions.

Effluent after treatment

17.5

>2.5mm

9737.0

PCB's in silt before and after microbiological treatment

4.1 Fractionation of silt enabled concentration of PCB's into approximately one third of the volume where the remaining fraction was correspondingly reduced in PCB level such as to be suitable for disposal by landfill.

Before treatment pglkg

31891 .l

4.2 The trial demonstrated that silt that is contaminated with PCB's and other organic moieties can be successfully treated to a standard whence the final liquid effluent contains negligible levels of PCB's and can be discharged to the sea and the silt could be landfilled without significant detriment to the environment.

Tb

50790.2

After treatment pglkg

3925.4

Tc

8550.8

Cleanup

87.70%

Td

64994.9

Te

553996.9

A Case Study North Blyth - Battleship Wharf Scheme

Colin Robson, Northumberland County Council

REMEDIATION OF CONTAMINATED RIVER SILTS

DON'T PANIC!

The problem of Contaminated Land in Britain is a serious one, however, the title of this presentation is, I think, appropriately called Don't Panic.

When I became involved with the Battleship Wharf Scheme in Northumberland there was great clamour from the Press, the Public and most of all the various Regulatory Bodies over the problems associated with the site.

There certainly were plenty of problems, after 85 years of shipbreaking the site was contaminated with 60,000 cubic metres of asbestos laden soils, heavy metals including lead, mercury and cadmium and worst of all transformer oils containing PCB's. The latter had been discharged onto the site and into the adjacent tidal dock and river from dismantled Soviet Warships.

Having worked for 25 years on contaminated land sites, mostly on former colliery areas, I was fully aware of the regulatory framework within which I would have to operate.

Less expected was the initially negative approach taken by NRA and MAFF especially in response to the PCB problem. Something I am pleased to say was quickly overcome.

The site is in the control of the Port of Blyth which is administered by a Board of Commissioners and a Chief Executive. When, following the discharge of oils, the Port were asked to deal with the problem they searched for a firm who could handle PCB's. A previous speaker at this symposium is an employee of a company who showed some knowledge of the problem and you have heard his approach. On my part, at that time, and still, I am not convinced that a cost effect treatment exists for this problem.

To understand what his company and later others were suggesting to me it was necessary to carry out a detailed trawl of the published literature on PCBs. This was done and has produced by purchase, borrowing and photocopying what is I guess one of the most comprehensive libraries on the topic available. That part was easy, reading it all, understanding it and trying to reconcile conflicting evidence and views was another matter.

One of the first lessons was that measurements of levels of PCBs, depending on the protocol used, could vary widely. Further, some of the levels of reduction required by MAFF were at the limits of detection technology.

The basic practical problem was that the MAFF would not issue a licence to tip dredged material at sea that contained PCBs at levels above 200 parts per billion. Such a licence is obviously vital to keep the Port operational. A chart of surveyed samples showed a contour of material above this level lying off the tidal dock, with a maximum of 50 parts per million in the dock. There was one plus factor here in that the River Blyth is a low energy system and silts do not move very far during the rise and fall of tides.

Following the initial stage of understanding the material we were dealing with , several things were evident and had to be agreed with the regulators:-

* The PCBs above the 200 parts per billion contour had to be brought ashore and treated.

* An environmentally safe method of dredging was necessary.

* A decision had to be taken regarding encapsulation or treatment.

* The sampling work had to be extended and refined.

At this point it was already obvious that there would have to be some encapsulation of contaminants on site. The site investigation had shown that the old quay was contaminated with a mix in the soil of asbestos, oils, heavy materials and PCBs. This mix meant that even if the technology for remediation was available, it would be very expensive. None of the contaminant levels on site could be classified as extremely high.

There is therefore still a solution to the problems of the dredged silts of including them in the stabilisation and encapsulation process.

The encapsulation was then considered and it was decide to construct a retaining bund across the old tidal dock behind which the contaminants could be encapsulated. This was later refined into a new quay wall with additional funds from the Port of Blyth.

At this construction was to be across open water it was decided to use a system of 13 metre diameter circular steel cells which required a level river bed as a formation. This design meant a sophisticated environmental and engineering dredging contract to first remove the contaminated silts and then allow clean silts and rock to be dredged and tipped to sea. This contract was prepared and put out to tender.

When the tenders were returned they were some £300,000 over estimate and the scheme was in jeopardy. The dredger however could never reach into the tidal dock so this was cleared by machine and dump trucks at low tide. A piece of good fortune at this time was exceptionally low tides which allowed clearance beyond the end of the tidal dock.

Simultaneously more refined results from sampling carried out by the NRA showed that 95% of total contamination was within the area that had been cleared. This threw into even greater relief the extra cost of "environmental dredging".

In discussion with the Port of Blyth's Engineer he identified that he operated a river bed "plough" which could move the contaminated silts within reach of an extended reach excavator. It was estimated that this would reduce the remaining contamination to 1-2% of the original total.

Whilst the river silts contained the lowest amounts of PCBs, they were in a ratio of 4 to 1 by volume with the tidal dock extract. However in terms of their concentration of PCBs they were no worse than other materials found in industrial areas nationally, being in the range 0.2 to 1 part per million.

Both the NRA and MAFF agreed this procedure and over a three week period the contaminated silts were brought ashore and stored in a temporary lagoon. It has been decided to dewater the river silts using a filter press system and the material will then be mixed with courser soils and used as general fill in non-developable areas of the site.

The jury is still out on the treatment of the tidal dock material. As I said earlier, I have yet to be convinced that a verifiable treatment for the reduction of PCBs to industrial background levels

exists. In support of this I would sight a recent conference in Maastricht on contaminated land treatment which in out of 100 papers and 150 poster presentations hardly mentions PCBs at all.

At present my preferred option remains encapsulation although whilst awaiting the bundldock walls construction, which will take 10 months, I remain open to offers.

However, I now feel confident that as a scientific layman, I can make a more considered judgement on those offers.

The British Waterways Experience

Nick Smith, British Waterways

Historical Perspective

The canal system of the UK dates from 1757 to the 1830s. The system was built to service the needs of the industrial revolution and transects many of the industrial heartlands of the UK.

In 1948, the majority of canals and waterways came under government control in the form of the British Transport Commission. The management of the canals and waterways passed to the successor body, British Waterways, in 1963.

Today the network of waterways under BW control is managed principally for leisure and tourism and as an environmental and heritage asset of national importance. Freight transport continues to be important on the broad river navigations and canals in the north east.

Dredging is an important part of the sustainable management of all canals and rivers navigations. It is necessary to provide for navigation and to maintain and enhance wildlife and fishery interest. Localised sections of waterway have sediments contaminated by historical industrial activity. Removal of this material is part of the on-going process of renewal which the waterways have enjoyed in recent years.

Development of Regulations

For most of the 200 years of canal history disposal of dredgings was an unregulated process. In 1988 dredgings lost their exempt status and were included within the definition of controlled waste. This change, together with additional regulations in 1992 and the obligations of the Duty of Care brought in the new requirements for the disposal of dredgings and the need to understand quality.

A further round of regulations implemented in 1994 brought in new requirements for the management of waste and its disposal and set out some specific exemptions applicable to inland dredging disposal.

Quantification of Liability

To establish an overview of the liability and determine disposal options it was important to obtain a qualitative of the material to be dredged.

Sediment Quality

Sediment sampling was carried out in the first months of 1992. Samples of sediment were taken every 2 km and submitted to an analytical laboratory.

The 30 parameters specified in the analytical suite were based on those previously requested by regulatory authorities.

The main parameters were interpreted against national codes of practice or guidance such as DOE Code of Practice for Agricultural Use of Sewage Sludge (DOE, 1989) and the ICRCL Guidance. In

addition guidance derived from Kelly (1979) and the Netherlands guidance (Ministry of Housing, Physical Planning and Environment, 1987) was used to evaluate parameters not covered by the existing government issued guidance.

These guidance documents were used to construct a classification system that would provide guidance on the disposal options. The classification system focuses on contamination issues and their potential environmental significance in disposal.

DecontaminationlTreatment Projects

Treatment plants have been used to screen and dewater dredgings principally because it is generally more difficult to dispose of wet dredgings than it is to dispose of contaminated material. As part of a process an element of decontamination may have been achieved by separating off the fines, which are usually associated with the higher levels of contamination, or by the inclusion of additives which bind in the contamination and reduce the potential for leaching at a future date.

A simple form of decontamination which BW has used, is to screen out the gross items, cans, bottles, traffic cones etc. from uncontaminated silt to allow it to be used for disposal on agricultural land.

Where we have identified silts which are heavily contaminated consideration is being given to processes which can remove the contaminating elements. These processes are:

(I) soil washing techniques using solvents or resins (J) immobilisation (K) bioremediation

Conclusions

Currently decontamination processes tend to be expensive when compared to the cost of landfill. This is exacerbated by the relatively small quantities generated during a BW dredging project and the problems associated with access for large equipment alongside the waterway network. As legislation tightens up, resulting in increased charges at landfill sites, plus the impending introduction of the Landfill Tax, decontamination will become more competitive.

Appendix 2 p-..p- ~

Mr S J Bamford Mr Steve Barber Mr Neville Burt Mr Mike Butcher Mr Bill Coles Mr Tim Denton MS Caroline Fletcher Mr Dudley Gibbs Mr Alan Hunter Mr Martin Kroezen Mr Peter Lucas MR James Maclean Mr lan Marmont Mr Richard Melhuish MS Eleni Paipai Mr Michael Pearson Dr John Rees Mr Gavin Ridding Dr Chris Riley Mr Colin Robson MR Eduard Slob Mr Nick Smith Mr Lode Speleer Mr Gerard Stokman Mr David Tonks Mr Steve Warren Dr Peter Wood Mr Philip Woodgate

List of participants

The Decontamination of Dredged Material

HR Wallingford

23 January 1996

ADAS AEA Technology HR Wallingford BHR Group Ltd The Bristol Port Company Maunsell LRDC HR Wallingford Biolytic Systems Ltd NRA Northumbria & Yorkshire Heijmans Milieutech Niek Bank Mersey Docks & Harbour Co. Land & Water Services Ltd British Waterways Land & Water Services Ltd HR Wallingford Tees & Hartlepool Port Authority Celtic Technologies London Docklands Dev. Corp. BHR Group Ltd Northumberland County Council Ham Dredging British Waterways Jan de Nul (UK) Ltd Ministry of Transport - Netherlands EDGE Consultants UK Ltd HR Wallingford AEA Technology Port of Sheerness Ltd

UK UK UK UK UK UK UK UK UK The Netherlands UK UK UK UK UK UK UK UK UK UK UK UK UK The Netherlands UK UK UK UK

Appendix 3 CATS Ill Congress, Oostend, Belgium March 1996

A paper titled "Decontamination of dredged material-is it really feasible?" was presented at the CATS Ill conference held in Oostend, Belgium, 18- 20 March 1996. An Abstract follows;

Decontamination technologies which alter contaminated dredged material properties such that they are suitable for sea disposal or beneficial use are desirable. However, the wide range of technologies researched are underdeveloped and relatively costly when compared to alternative options, such as disposal at landfill sites. In this paper examples of contaminated dredged material in the U. K are given and a brief description of the international situation for decontamination technologies. The criteria which any prospective technology must satisfy in terms of practicality, effectiveness, economics and environmental acceptability, as well as meeting legislative requirements, are also outlined. An assessment of promising technologies for dredged material decontamination against outlined criteria has been undertaken. Existing and innovative technologies are more likely to develop if legislatively driven and if a real future for their requirement, against alternative options, is demonstrated. Further research and development is required, and although in industrially developed countries the handling of contaminated sediments is becoming a decreasing problem as source inputs are controlled, in developing countries, who are even less able to afford clean-up technologies, contamination of navigable waterways is still occurring and decontamination technologies will be needed.

The CATS Ill Congress was an international conference specifically aimed at treatment technologies for contaminanted dredged material and sewage sludge. It was an excellent opportunity to update information on more recent (last 2 years or so) reasearch which has been undertaken in other countries. The conference included representatives from all of the major countries involved in this field (Holland, Germany, Belgium, USA, Canada). HR Wallingford was however the only representatives from the UK with an interest in dredged material decontamination. Severn Trent were the only other representatives and their interests were specifically directed at sewage sludge incineration and disposal on agricultural land.